The pore configuration in porous medium is assumed to be the randomly distributed cube-like particles which can overlap each other in the periodic cubic domain, and the impact of particle characteristics on the percol...The pore configuration in porous medium is assumed to be the randomly distributed cube-like particles which can overlap each other in the periodic cubic domain, and the impact of particle characteristics on the percolation property of these cube-like particle packing systems is analyzed.Firstly, by combining the percolation models and finite-size scaling analysis, three numerical parameters(i.e., percolation transition width △L, local percolation threshold ψ_c(L), and correlation length exponent v) for the cube-like particle systems with shape parameter s in[1.0, +∞] are derived successively. Then, based on the relation between the percolation thresholdψ_c in infinite space and the local percolation threshold ψ_c(L), the corresponding ψ_c with s in[1.0, +∞] are further determined. It is shown from the study that the characteristics of cube-like particles have significant influence on the global percolation threshold ψ_c of the particle packing systems. As the parameter s increases from 1.0 to +∞, the percolation threshold ψ_c will go down persistently. When the surface of cube-like particles is cubical and spherical, respectively, the minimum and maximum thresholds ψ_c,min and ψ_c,max are obtained.展开更多
High activity catalyst with simple low-cost synthesis is essential for fuel cell commercialization. In this study, a facile procedure for the synthesis of cube-like Pt nanoparticle （PtCube） composites with high surf...High activity catalyst with simple low-cost synthesis is essential for fuel cell commercialization. In this study, a facile procedure for the synthesis of cube-like Pt nanoparticle （PtCube） composites with high surface area carbon supports is developed by mixing precursor of Pt with carbon supports in organic batches, hence, one pot synthesis. The PtCube grow with Vulcan XC-72 or Ketjen black, respectively, and then treated for 5.5 h at 185℃ （i.e., Ptcube5.5/V and PtcubeS.5/K）. The resulting particle sizes and shapes are similar; however, Ptcube5.5/K has a larger electrochemical active surface area （EASA） and a remarkably better formic acid （FA） oxidation performance. Optimization of the PtCube/K composites leads to Ptcubelo/K that has been treated for 10 h at 185℃. With a larger EASA, Ptcubelo/K is also more active in FA oxidation than the other Ptcube/K composites. Impedance spectroscopy analysis of the temperature treated and asprepared （i.e., untreated） Ptcube/K composites indicates that PtCube10/K is less resistive, and has the highest limiting capacitance among the PtCube/K electrodes. Consistently, the voltammetric EASA is the largest for Ptcube 10/K. Furthermore, PtCube10/K is compared with two commercial Pt/C catalysts, Tanaka Kikinzoku Kogyo （TKK）, and Johnson Matthey （JM）Pt/C catalysts. The TKK Pt/C has a higher EASA than Ptcube10/K, as expected from their relative particles sizes （3-4 nm vs. 6-7 nm for PtcubelO/K）, however, Ptcube10/K has a significantly better FA oxidation activity.展开更多
Transition metal carbides have been shown to exhibit good catalytic performance that depends on their compositions and morphologies,and understanding such catalytic properties requires knowledge of their precise geome...Transition metal carbides have been shown to exhibit good catalytic performance that depends on their compositions and morphologies,and understanding such catalytic properties requires knowledge of their precise geometry,determination of which is challenging,particularly for clusters formed by multiple elements.In this study,we investigate the geometries and electronic structures of binary V_(n)C_(3)-(n=1-6)clusters and their neutrals using photoelectron spectroscopy and theoretical calculations based on density functional theory.The adiabatic detachment energies of V_(n)C_(3)-,or equally,the electron affinities of V_(n)C_(3),have been determined from the measured photoelectron spectra.Theoretical calculations reveal that the carbon atoms become separate when the number of V atoms increases in the clusters,i.e.,the C-C interactions present in small clusters are replaced by V-C and/or V-V interactions in larger ones.We further explore the composition dependent formation of cubic or cube-like structures in 8-atom VnCm(n+m=8)clusters.展开更多
We prove that a locally compact ANR-space X is a Q-manifold if and only if it has the Disjoint Disk Property (DDP), all points of X are homological Z∞-points and X has the countable-dimensional approximation property...We prove that a locally compact ANR-space X is a Q-manifold if and only if it has the Disjoint Disk Property (DDP), all points of X are homological Z∞-points and X has the countable-dimensional approximation property (cd-AP), which means that each map f:K→X of a compact polyhedron can be approximated by a map with the countable-dimensional image. As an application we prove that a space X with DDP and cd-AP is a Q-manifold if some finite power of X is a Q-manifold. If some finite power of a space X with cd-AP is a Q-manifold, then X2 and X×[0,1] are Q-manifolds as well. We construct a countable familyχof spaces with DDP and cd-AP such that no space X∈χis homeomorphic to the Hilbert cube Q whereas the product X×Y of any different spaces X, Y∈χis homeomorphic to Q. We also show that no uncountable familyχwith such properties exists.展开更多
基金financially supported by the National Natural Science Foundation of China (Grants 51878152 and 51461135001)the Ministry of Science and Technology of China "973 Project" (Grant 2015CB655102)
文摘The pore configuration in porous medium is assumed to be the randomly distributed cube-like particles which can overlap each other in the periodic cubic domain, and the impact of particle characteristics on the percolation property of these cube-like particle packing systems is analyzed.Firstly, by combining the percolation models and finite-size scaling analysis, three numerical parameters(i.e., percolation transition width △L, local percolation threshold ψ_c(L), and correlation length exponent v) for the cube-like particle systems with shape parameter s in[1.0, +∞] are derived successively. Then, based on the relation between the percolation thresholdψ_c in infinite space and the local percolation threshold ψ_c(L), the corresponding ψ_c with s in[1.0, +∞] are further determined. It is shown from the study that the characteristics of cube-like particles have significant influence on the global percolation threshold ψ_c of the particle packing systems. As the parameter s increases from 1.0 to +∞, the percolation threshold ψ_c will go down persistently. When the surface of cube-like particles is cubical and spherical, respectively, the minimum and maximum thresholds ψ_c,min and ψ_c,max are obtained.
文摘High activity catalyst with simple low-cost synthesis is essential for fuel cell commercialization. In this study, a facile procedure for the synthesis of cube-like Pt nanoparticle （PtCube） composites with high surface area carbon supports is developed by mixing precursor of Pt with carbon supports in organic batches, hence, one pot synthesis. The PtCube grow with Vulcan XC-72 or Ketjen black, respectively, and then treated for 5.5 h at 185℃ （i.e., Ptcube5.5/V and PtcubeS.5/K）. The resulting particle sizes and shapes are similar; however, Ptcube5.5/K has a larger electrochemical active surface area （EASA） and a remarkably better formic acid （FA） oxidation performance. Optimization of the PtCube/K composites leads to Ptcubelo/K that has been treated for 10 h at 185℃. With a larger EASA, Ptcubelo/K is also more active in FA oxidation than the other Ptcube/K composites. Impedance spectroscopy analysis of the temperature treated and asprepared （i.e., untreated） Ptcube/K composites indicates that PtCube10/K is less resistive, and has the highest limiting capacitance among the PtCube/K electrodes. Consistently, the voltammetric EASA is the largest for Ptcube 10/K. Furthermore, PtCube10/K is compared with two commercial Pt/C catalysts, Tanaka Kikinzoku Kogyo （TKK）, and Johnson Matthey （JM）Pt/C catalysts. The TKK Pt/C has a higher EASA than Ptcube10/K, as expected from their relative particles sizes （3-4 nm vs. 6-7 nm for PtcubelO/K）, however, Ptcube10/K has a significantly better FA oxidation activity.
基金the Doctoral Start-up Funding of Zhengzhou University of Light Industry(No.2017BSJJ030)Henan Province Science Fund for Excellent Young Scholars(No.202300410494)+4 种基金the Beijing Municipal Science and Technology Commission(No.Z191100007219009)for supportsthe VSC(Flemish Supercomputer Center),funded by the Research Foundation-Flanders(FWO)the Flemish Government-department EWIthe support of Xi’an Jiaotong University via the“Young Talent Support Plan”the“Fundamental Research Funds for Central Universities”。
文摘Transition metal carbides have been shown to exhibit good catalytic performance that depends on their compositions and morphologies,and understanding such catalytic properties requires knowledge of their precise geometry,determination of which is challenging,particularly for clusters formed by multiple elements.In this study,we investigate the geometries and electronic structures of binary V_(n)C_(3)-(n=1-6)clusters and their neutrals using photoelectron spectroscopy and theoretical calculations based on density functional theory.The adiabatic detachment energies of V_(n)C_(3)-,or equally,the electron affinities of V_(n)C_(3),have been determined from the measured photoelectron spectra.Theoretical calculations reveal that the carbon atoms become separate when the number of V atoms increases in the clusters,i.e.,the C-C interactions present in small clusters are replaced by V-C and/or V-V interactions in larger ones.We further explore the composition dependent formation of cubic or cube-like structures in 8-atom VnCm(n+m=8)clusters.
基金This work was supported by the Slovenian-Ukrainian(Grant No.SLO-UKR 04-06/07)
文摘We prove that a locally compact ANR-space X is a Q-manifold if and only if it has the Disjoint Disk Property (DDP), all points of X are homological Z∞-points and X has the countable-dimensional approximation property (cd-AP), which means that each map f:K→X of a compact polyhedron can be approximated by a map with the countable-dimensional image. As an application we prove that a space X with DDP and cd-AP is a Q-manifold if some finite power of X is a Q-manifold. If some finite power of a space X with cd-AP is a Q-manifold, then X2 and X×[0,1] are Q-manifolds as well. We construct a countable familyχof spaces with DDP and cd-AP such that no space X∈χis homeomorphic to the Hilbert cube Q whereas the product X×Y of any different spaces X, Y∈χis homeomorphic to Q. We also show that no uncountable familyχwith such properties exists.
